TRF1-labeled chromatin reveals that telomeres form loops.
Telomeres protect chromosome ends from degradation and shortening, but they must themselves be protected from repair systems that recognize free DNA ends. Images of telomere DNA, lacking its chromatin components, suggested that its protection might be enhanced by looping and insertion of the telomere's single-stranded overhang into the double-stranded telomeric repeats. Wrapping this loop up in chromatin proteins probably hides the overhang from agents that detect free ends, but because telomere chromatin is difficult to extract from the nuclear matrix, whether chromatin looping occurs was unknown.
The authors have conquered the chromatin extraction problem by using two types of blood cells that have fewer proteins gluing the chromatin to the matrix. After digesting away nontelomeric DNA, the authors labeled...
